1. Field of the Invention
The present invention relates to a method of manufacturing a piezoelectric actuator and a liquid ejection head, and more particularly to a method of manufacturing a piezoelectric actuator in which a piezoelectric film is arranged between two electrode films, and a liquid ejection head comprising this piezoelectric actuator.
2. Description of the Related Art
Japanese Patent Application Publication No. 2001-113712 discloses a method of manufacturing an inkjet head in which films of an electrode member, a piezoelectric member and a diaphragm member are deposited onto each of a plurality of substrates, and the diaphragm member on the plurality of substrates after the film deposition is bonded with a pressure chamber component having a surface area that is broader than the combined surface area of the plurality of substrates.
Japanese Patent Application Publication No. 2002-217468 discloses a method of manufacturing an electronic component in which a first electrode is formed on one surface of a piezoelectric member layer, a second electrode having a substrate for thin film formation is formed on the other surface of the piezoelectric member layer, and the substrate for the thin film formation is then removed from the second electrode by using an etching liquid.
In the related art, there is known a piezoelectric actuator having a multiple-element structure in which a plurality of piezoelectric elements are formed on one substrate. The piezoelectric actuator is used in a liquid ejection head (inkjet head) of an inkjet recording type, for example.
When a film of piezoelectric material (e.g., Pb (lead) zirconate titanate (PZT)) is deposited on a substrate, the properties of the piezoelectric film thus deposited are greatly affected by the substrate on which the film is deposited and the layers interposed between the substrate and the piezoelectric film. For example, the stress applied to the piezoelectric film by the substrate or the interposed layer gives rises to cracking in the piezoelectric film, affects the so-called piezoelectric constant, and also affects the long-term reliability of the piezoelectric film.
At present, liquid ejection heads which have a large number of nozzles per unit surface area (a high nozzle density) are sought. When driving a liquid ejection head having a high nozzle density, since a large number of piezoelectric elements are driven simultaneously in comparison with the related art, it is necessary to reduce the electrical resistance of the wiring portions that supply electricity to the piezoelectric elements. However, if a lower electrode (common electrode) and a piezoelectric film are formed on a substrate of insulating material (e.g., silicon (Si)), then it is difficult to reduce the electrical resistance of the lower electrode.
Neither Japanese Patent Application Publication No. 2001-113712 nor Japanese Patent Application Publication No. 2002-217468 resolves the problem of reducing the electrical resistance of the wiring portions. In Japanese Patent Application Publication No. 2001-113712, a diaphragm is deposited as a film and bonded to a pressure chamber component; however, if a diaphragm of several micrometers (μm) or greater is deposited, then it is difficult to control the stress in the diaphragm. Moreover, if the deposited diaphragm is bonded as in Japanese Patent Application Publication No. 2001-113712, then there is a risk of variation in performance between the respective piezoelectric elements, due to non-uniformity in the thickness of the adhesive. Furthermore, it is also difficult to achieve matching with other processes. In Japanese Patent Application Publication No. 2002-217468, as well as the fact that the deposition substrate is wasted, it is also difficult to achieve matching with other processes.
One possible way of reducing the electrical resistance of the lower electrode (common electrode) is to increase the film thickness of the lower electrode. However, if the thickness of the lower electrode is increased, then stress in the film becomes more difficult to control and there is a drawback in that the reliability of the piezoelectric elements declines.